1. Field of the Invention
The invention relates generally to reluctance machines, and more specifically, to a foil coil switched reluctance machine and a food waste disposer employing a switched reluctance machine.
2. Description of Related Art
Reluctance machines are well known in the art. In general a reluctance machine is an electric machine in which torque is produced by the tendency of a movable part to move to a position where the inductance of an excited winding is maximized (i.e., the reluctance is minimized).
In one type of reluctance machine the phase windings are energized at a controlled frequency. This type of reluctance machine is generally referred to as a synchronous reluctance machine. In another type of reluctance machine, circuitry is provided to determine the position of the machine""s rotor, and the windings of a phase are energized as a function of rotor position. This type of reluctance machine is generally referred to as a switched reluctance machine. Although the description of the current invention is in the context of a switched reluctance machine, the present invention is applicable to all forms of reluctance machines, including synchronous and switched reluctance motors and to other machines that have phase winding arrangements similar to those of switched reluctance machines.
The general theory of design and operation of switched reluctance machines is well known and discussed, for example in xe2x80x9cThe Characteristics, Design and Applications of Switched Reluctance Motors and Drives,xe2x80x9d by Stephenson and Blake, presented at the PCIM ""93 Conference and Exhibition at Nuremberg, Germany, Jun. 21-24, 1993.
In general, known reluctance machines have been designed with a stator yoke having inwardly projecting salient poles. The rotor also defines salient poles and typically contains no circuitry or permanent magnets. The rotor and the stator are coaxial. Associated with each stator pole is a coil of wire wound around the pole. The stator poles, which are positioned opposite one another, are generally coupled to form one or more phases. A phase is energized by delivering current to the coil. Switching devices are generally provided which allow the coil to be alternately connected into a circuit which delivers current to the coil when the phase is energized and one which separates the coil from a current source when the phase is de-energized, and which may recover energy remaining in the winding.
Reluctance torque is developed in a reluctance machine by energizing a pair of stator poles when a pair of rotor poles is in a position of misalignment with the energized stator poles. The degree of misalignment between the stator poles and the rotor poles is called the phase angle. Energizing a pair of stator poles creates a magnetic north and south in the stator pole pair. Because the pair of rotor poles is missaligned with the energized stator poles by some phase angle, the inductance of the stator and rotor is less than maximum. The pair of rotor poles will tend to move to a position of maximum inductance with the energized windings. The position of maximum inductance occurs when the rotor and stator poles are aligned.
At a certain phase angle in the rotation of the rotor poles to the position of maximum inductance, but typically before the position of maximum inductance is achieved, the current is removed from the phase de-energizing the stator poles. Subsequently, or simultaneously, a second phase is energized, creating a new magnetic north and south pole in a second pair of stator poles. If the second phase is energized when the inductance between the second pair of stator poles and the rotor poles is increasing, positive torque is maintained and the rotation continues. Continuous rotation is developed by energizing and de-energizing the stator poles in this fashion. The total torque of a reluctance machine is the sum of the individual torques described above.
In general, most known reluctance machines have been designed with a stator yoke having inwardly projecting salient poles and a hollow core area. Nested concentrically in the hollow core area, or stator bore, is a rotor having outwardly projecting salient poles, defining a radial air gap between the rotor and stator poles. The rotor is connected to a rotor shaft that is free to rotate and acts as an output shaft when the machine is motoring, and as an input shaft when the machine is generating. The stator and rotor are typically constructed from stacks of laminations stamped from a magnetic material to reduce eddy current losses, among other things. The axial length of such conventional switched reluctance machines is not suitable for many applications. Further, the laminated construction of typical reluctance machines complicates the assembly process.
The present invention addresses shortcomings associated with the prior art.
The present invention relates to reluctance electric machines such as motors and generators, and more particularly to a variable reluctance machine designed for efficient operation and improved volumetric efficiency by using foil coil, concentrated stator pole windings on a solid or semi-solid salient pole stator, a minimum axial air gap and a solid, salient pole disc-shaped rotor. This unit is more easily produced than a more conventional laminated structure. The eddy current losses may be higher than a conventional laminated structure as is found in the prior art, but applications such as food waste disposers, sump pumps, ceiling fans, furnace blower motors, etc. have water or air cooling integral to the product.
In accordance with aspects of the present invention, a switched reluctance machine includes a stator having an annular support member with a plurality of stator poles disposed there on. The stator poles each comprise a corresponding foil coil stator winding. A solid disc-shaped rotor defines a plurality of salient rotor poles. The rotor is rotatably positioned opposite the support member to establish an axial air gap between the rotor and stator poles. A control circuit controls energization of the phase windings to create torque.
In accordance with further aspects of the invention, a food waste disposer incorporates a switched reluctance machine, and includes an inlet for receiving food waste, a grinding plate connected to a rotatable shaft, and a switched reluctance motor operable to drive the shaft and thus, the grinding plate to grind food waste received via the inlet into particulate matter. In exemplary embodiments, the switched reluctance motor includes a stator having a plurality of stator poles disposed therein, where each stator pole comprises a corresponding foil coil stator winding. A solid disc-shaped rotor defines a plurality of salient rotor poles, and the rotor is rotatably positioned proximate the stator to establish an axial air gap between the rotor and stator poles. The grinding plate may be integrally formed with the rotor.
In certain embodiments of the invention, a food waste disposer includes an inlet for receiving food waste, a stationary shredder ring, and a grinding plate situated adjacent the stationary shredder ring. The grinding plate has first and second sides, with the first side having at least one lug attached thereto. The second side has a plurality of rotor poles formed therein. A stator includes a plurality of stator poles disposed therein, each of which is formed from a corresponding foil coil stator winding. A shaft is rotatably received by the stator, and the grinding plate is fixed to the shaft to rotate therewith such that the grinding plate and the stator form an axial air gap therebetween. The stator may be sealed relative to the shaft and grinding plate to allow particulate matter and water to flow from the grinding plate over the stator.